Pumps used on ABS and TCS applications are generally known, for example, in U.S. Pat. No. 5,249,935 one such pump is described. In pumps of this type, inlet bores and outlet bores terminate into cylinders, and pressure fluid, controlled by valves, is supplied from the inlet bores to the outlet bores through pistons moving in the longitudinal direction of the cylinders. The pistons are driven by an electric motor through an eccentric, the drive chamber being sealed in relation to the compression space by the seals of the pistons.
In spite of the presence of the piston seals small quantities of pressure fluid are entrained by the moving surface of the pistons through the seals into the space surrounding the eccentric. Normally, atmospheric pressure is present in this space. The entrainment of small quantities of pressure fluid may gradually cause pressure fluid to accumulate in the ambient space of the eccentric, in which case the piston plunges into the accumulated pressure fluid. This plunging causes pressure pulsations. These pressure pulsations may urge pressure fluid into the inner space of the driving electric motor and eventually destroy it.
As a remedy, it has been suggested to provide a bore from the ambient space of the eccentric through the pump housing in order to impart an exit conduit to the introduced pressure fluid. However, such a connection is disadvantageous when the pump assembly is arranged in the automotive vehicle at a comparatively low level in respect of the road surface. It has to be expected in these cases that liquid from the road is carried into the connecting conduit and, subsequently, into the ambient space of the eccentric. The resulting contamination may rapidly destroy the very finely machined working surfaces of the eccentric and the pistons. Further, the ingress of liquid may eventually lead to the destruction of the electric motor by causing a short circuit. This applies in particular to vehicles from which it is demanded that they can pass through high water levels.
Therefore a primary object of the present invention is to render a pump assembly of this type reliably leak-proof by simple means.
The present invention achieves this objective by placing a non-return valve in the connecting conduit between the ambient space of the eccentric and the exit aperture of the pump housing, this non-return valve being arranged below the ambient space in the assembly position.
This way, it is possible to provide a discharge from the pump housing of the pressure fluid which bypassed the piston and collected in the ambient space, and to prevent the ingress of ambient fluid such as road liquids into the pump housing at the same time.
In order to reliably prevent the accumulation of entrained pressure fluid in the ambient space of the eccentric, it is preferable to use the accumulating pressure fluid itself to force the non-return valve to open.
A particularly reliable design of the non-return valve is achieved by using the force of gravity acting upon the quantity of accumulated pressure fluid to open the valve so that a damaging accumulation of pressure fluid will not occur.
To facilitate the mounting of the non-return valve and to better adapt the leak-proof capacity of a vehicle to the respective requirements, it is preferred that the valve member has a sealing edge engaging the pump housing.
A particularly simple structure of the non-return valve is made possible by the present invention in that no special means is needed for generating the preload on the piston seal. Instead, the presence of the seal in the valve housing and the characteristics of this seal itself ensure sufficient contact pressure on the sealing seat.
A fastening bore in the pump housing, which extends substantially horizontally in the installation position, is simultaneously utilized as an exit for the connecting conduit. As a result, the connecting conduit has a relatively narrow, angular course, a type of labyrinth being formed which, additionally, contributes to improving the present invention by preventing the direct ingress of spray water and dirt.